Question

Assertion: The two strands of DNA are complementary to each other.
Reason: Adenine specifically forms hydrogen bonds with guanine whereas cytosine forms hydrogen bonds with thymine
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

Answer 1

Hint: The question is about DNA and the bonds present between the two strands of it. So, basically DNA is double stranded genetic material found in the living organisms and also few viruses. These strands are made of many nucleotides. A nucleotide is made up of a nitrogen base, phosphate group and deoxyribose sugar. There are four nitrogen bases which are mentioned in the reason part.

Complete answer:
By now, you have got an idea about DNA. Basic knowledge on DNA is quite enough to answer the question.Every nucleotide one strand pairs up with the nucleotide of the opposite strand. So,four nitrogen bases are involved namely Adenine,Guanine which are purines and Cytosine and Thymine are pyrimidines. Every adenine present on one nucleotide pairs up with Thymine on another strand by forming two hydrogen bonds whereas Guanine pairs up with Cytosine by three hydrogen bonds. So, if you know the nucleotide sequence of one strand,the sequence of another strand can be known,this phenomenon is called complementary. Hence, the assertion is right. In the reason it is mentioned that Adenine pairs with guanine which is absolutely wrong. By this,you can conclude that the assertion is correct and reason is wrong.

Hence the correct answer is option C

Note:
DNA is Deoxyribonucleic acid. A purine always base pairs with pyrimidine, which means if there is purine on one strand of DNA, there should be pyrimidine on the other strand. This base pairing helps us to know the nucleotide sequence of template strands using a complementary strand. There are three billion such base pairs in the human genome.